1. Field of the Invention
This invention relates to a catadioptric lens barrel which can be attached to an optical projection unit, such as a projection exposure apparatus used to manufacture semiconductor wafers. More particularly, the present invention relates to a catadioptric lens barrel structure including its support structure, the lens barrel structure comprising a plurality of lens barrels aligned in parallel, and at least one transverse lens barrel connecting the plurality of lens barrels.
2. Description of the Related Art
A lens barrel is a tubular mechanical structure containing a series of lenses which are aligned to transfer an image from one end of the lens barrel to the other. The lens barrel may include a sturdy threaded body and durable metal retaining rings, often referred to as sub-barrels, to carry a series of lens holders, commonly referred to as cells. Another type of lens barrel is known as a catadioptric lens barrel. A catadioptric lens barrel contains not only refractive elements, such as lenses, but also reflective elements, such as mirrors.
Both of these lens barrel designs are used in conventional optical systems. For example, optical projection units often have a lens barrel and may be used in a projection exposure apparatus for production of semiconductor wafers. The projection exposure apparatus includes a reticle positioned near an entrance end of the lens barrel and a semiconductor wafer positioned near an exit end. The projection exposure apparatus shines light through the reticle, photographically reduces a pattern on the reticle, and sequentially transfers the pattern, through the lens barrel, onto a predetermined area on the semiconductor wafer. The semiconductor wafer is a silicon wafer with a photo-sensitive coating for making semiconductor devices, such as microprocessor or memory chips.
A catadioptric lens barrel system using two or more lens barrels, arranged in parallel, offers benefits not found in conventional single barrel systems. The parallelism of the lens barrels reduces the overall height of the lens barrel, but increases the overall width. Reduced height is important for many reasons, such as for ease of transport. This type of catadioptric lens barrel design, however, poses several problems. First, keeping proper alignment of a plurality of lens barrels can be difficult. Second, the focus depth of the projection system changes as temperature changes. Coefficients of thermal expansion of the lens barrels, including their internal components, and the indices of refraction of all lens materials vary with temperature. Errors related to these factors collectively alter the focusing properties of the optical system. Third, the lens barrel structure tends to be more sensitive to movement or vibration than conventional single barrel designs.
In light of the foregoing, there is a need for a catadioptric lens barrel structure that holds the lens barrels stabily and accurately, and minimizes distortion errors due to temperature changes, vibrational, or other external forces, so that the resulting image remains focused as it is transferred and reduced from the reticle to the semiconductor wafer.
The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the principles of the invention, as embodied and broadly described herein, one embodiment of the invention is directed to a lens barrel structure comprising a plurality of lens barrels, a support structure for supporting the plurality of lens barrels, and a plurality sets of flexures for resiliently securing the plurality of lens barrels to the support structure.
The present invention is also directed to a lithography system such as for use in a semiconductor manufacturing including the lens barrel structure as described above.
The present invention is further directed to a method for making a lens barrel structure, comprising the steps of providing a plurality of lens barrels, providing a support structure for supporting the plurality of lens barrels, and providing a plurality sets of flexures for resiliently securing the plurality of lens barrels to the support structure.
A first aspect of the present invention is directed to a lens barrel support structure for use in a projection exposure apparatus for stabily holding the lens barrels. The plurality of lens barrels include first and second lens barrels. The first lens barrel has a length, a first optical axis along the length of the first lens barrel, and a first optical pivot point along the first optical axis near a reticle located at one end of the first lens barrel. Similarly, the second lens barrel has a length, a second optical axis along the length of the second lens barrel, and a second optical pivot point along the second optical axis near a wafer located at one end of the second lens barrel. The first and second optical pivot points determine the optically optimum locations to hold the first and second lens barrels, respectively, to minimize thermal and vibrational effects. The first and second optical pivot points are calculated according to a computerized analysis or are generated by computer modeling. The first and second optical axes run parallel to each other and define a frontal plane. A first optical plane is defined as a plane perpendicular to the frontal plane and passing through the first optical axis. A second optical plane is defined as a plane perpendicular to the frontal plane and passing through the second optical axis. The lens barrel support structure comprises upper and lower support platforms. For maximum control, the upper support platform firmly secures the first lens barrel substantially near the first optical pivot point, and the lower support platform firmly secures the second lens barrel substantially near the second optical pivot point. The upper support platform is perpendicular to the first and second optical axes. The upper support platform has openings that accommodate the lens barrels. A second set of flexures resiliently secure the second lens barrel to the upper support platform. Likewise, the lower support platform is parallel to the upper support platform. The lower support platform has openings that accommodate the lens barrels. A first set of flexures resiliently secure the first lens barrel to the lower support platform.
A second aspect of the present invention is also directed to a lens barrel structure for use in a projection exposure apparatus. The second aspect of the invention derives from a more practical design to result in a support structure that is sturdier and easier to build from a mechanical stand point. Because of their size and weight, the lens barrels are best supported around their base and upper portions. Similar to the first aspect of the invention, the plurality of lens barrels comprises first and second lens barrels. Each lens barrel has a length and an optical axis. The first and second optical axes run parallel to each other and define a frontal plane. A first optical plane is defined as a plane perpendicular to the frontal plane and passing through the first optical axis. A second optical plane is defined as a plane perpendicular to the frontal plane and passing through the second optical axis. The lens barrel support structure comprises a base support platform and an upper support platform. The base platform firmly secures base portions of the plurality of lens barrels. The base platform is perpendicular to the first and second optical axes. The base platform has openings to accommodate the lens barrels. The upper support platform is parallel to the base platform, and has a plurality of openings to accommodate the lens barrels. A plurality of sets of flexures resiliently secure the first and second lens barrels to the upper support platform.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
Additional advantages will be set forth in the description which follows, and in part will be understood from the description, or may be learned by practice of the invention. The objects and advantages may be obtained by means of the combinations set forth in the attached claims.